"Well, it looks like a miracle that anything was accomplished given the lack of any constitution to spell out procedures.

Weird, I always thought the UK was a "constitutional monarchy." It's really hard to read the tea leaves from our side of the great pond."

The UK does have a constitution but it is not in single rigid written down form as much as being based on recognised procedure and president. This makes it more complicated but also more flexible. The procedure is that the incumbant remains PM until someone is in a position to do the job - and it appears that has happened after only 5 days which is actually quite quick considering it was over the weekend too. Theoretically the monarch has the power to invite someone to try and form a govt but in practice the palace does everything in its power to keep completely out of politics so she is only going through symbolic motions. So yes we are a constitutional monarchy where the monarch is our symbolic Head of State. She is not a politician and her job is to stay out of politics and basically do as she is expected. The convention is also that the politicians act in a way not to risk the need of putting the monarch (who is after all unelected)in any potential situation where she becomes involved in politics in any way.
It may seem airy-fairy to folk used to a written document, and there are plenty folk in the UK who would like to see a written constitution, but the reason it is still as it is and not a great hot issue is because by and large it kind of works. If the monarch actually became involved in politics then the fact she is unelected would become a hot issue hence the reluctance of the palace to get involved.